1. Field of the Invention
This invention relates generally to the field of laser vision correction and laser eye surgery, and more specifically to a device, system and methods for alignment of diagnostic and treatment images of the eye for more accurate surgical outcomes and improved patient satisfaction.
2. Description of Related Art
The popularity of photorefractive surgery for the correction or enhancement of vision continues to rise. Techniques such as photorefractive keratotomy (PRK), laser in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK) and variations thereof are now commonly used to correct the effects of nearsightedness (myopia), farsightnesses (hyperopia), and astigmatism, in addition to more traditional retinal surgery and other ocular surgical procedures. These vision defects are typically treated by laser ablating the cornea to steepen or flatten it according to its deviation from a geometry that is expected provide normal vision. A topography device such as, e.g., an Orbscan® corneal topographer (Bausch & Lomb/Orbtek, Salt Lake City, Utah) is routinely used to acquire the diagnostic information about the shape and other characteristics of the cornea. A surgeon can then use a laser programmed with this topographic information to appropriately ablate the corneal surface.
Basically, hyperopia and myopia, and astigmatism, are known as lower order aberrations referred to as defocus and cylinder, respectively. It is well known that higher order aberrations in addition to lower order aberrations degrade vision quality. Typical higher order aberrations include spherical aberration, coma, and compound astigmatisms. It is possible to measure these higher order aberrations with wavefront measuring devices such as disclosed in Williams U.S. Pat. No. 5,777,719 (incorporated herein by reference in its entirety), which describes an aberrometer instrument incorporating a Hartmann-Shack wavefront sensor to quantify higher order aberrations in the eye. The diagnostic measurement of higher order aberrations has lead to the ongoing development of systems and methods for customized ablation of the cornea and lenses used in or on the eye. The goal of customized ablation is to provide ever increasing visual quality in terms of acuity and contrast sensitivity (sometimes referred to as supernormal vision), as well as consistent image quality.
The technical advances in diagnostic equipment and treatment systems including lasers and eye trackers have also increased the accuracy required in making the diagnostic measurements and performing the treatments which are guided by these measurements. For example, it is desirable to obtain a diagnostic wavefront measurement of a patient's eye when the eye's pupil is dilated. Certain of the higher order aberrations that are suspected to cause glare or halos at night manifest themselves in the dilated (dark adapted) pupil. Therefore, a wavefront measurement with a wavefront sensing instrument is performed in a darkened environment such that the patient has a naturally dilated pupil. The measurement of the wavefront aberrations of the eye is obtained with respect to a reference point which is typically the pupil center or alternatively, a visual axis aligned to a fixation target in the diagnostic device. At the laser treatment stage, however, the nature and amount of light striking the eye from light sources in the treatment system environment typically causes the pupil to constrict. A complication arises because the center location of the dilated pupil is shifted from the center location of the constricted pupil. Thus, a calculated laser treatment centered on the constricted (treatment) pupil, based upon a diagnostic measurement aligned to the center of the dilated pupil, is likely to be applied at an incorrect location on the cornea.
Another complication arises from the fact that the position of a patient's eye in a sitting position rotates about an axis when the patient is in a treatment (supine) position. This is problematic because customized ablation treatment for higher order aberrations is not necessarily symmetric about an axis over the corneal surface. Moreover, a patient's head may have rotated between two diagnostic or eye image measurements separated in time, resulting in potential misalignment of a laser treatment. As such, both a translation and rotation of the eye must be accounted for between the diagnostic evaluation of the eye and the treatment stage.
One technique being developed to address these issues is referred to as iris pattern recognition. Rotation of the eye, for example, can sometimes be measured by identifying iris patterns using markers (artificial) or landmarks (natural). Since each person's iris is as unique as their fingerprints, it is proposed that various iris landmarks can be used to identify changing eye orientation. The reader is referred to the web site addresses: http://www.iriscan.com and http://schorlab.berkeley.edu for further information about iris pattern identification and eye movement. Notwithstanding that iris landmarks remain constant over the lifetime of the individual, it has been found that often the change in pupil size between diagnostic evaluation (dilated) and the treatment phase (constricted) is sufficient to deform or otherwise obscure the landmark, making it undetectable by conventional iris recognition software between diagnostic evaluation and treatment. Since it is highly desirable to be able to align the photoablative treatment of the cornea or other eye sites with the diagnostic measurement reference upon which it is based, there is a recognized need for methods and apparatus to acquire and maintain accurate alignment. A solution is proposed in applicant's co-pending patent application PCT/EP00/10373 which is incorporated herein in its entirety. That application discusses associating an artificially applied marker with diagnostic stage and therapeutic stage iris images in order to align these images at treatment. Thermal and dye based marks, for example, are suggested as artificial markers. It is appreciated, however, that patient discomfort, efficiency and accuracy are some disadvantages of current iris recognition and alignment means.
Accordingly, a need exists for devices, systems and methods to accurately account for the eye movement occurring between the diagnostic evaluation and treatment stages of laser eye surgery. The invention, while not limited as such, will be discussed in relation to laser vision correction such as LASIK, for example.